SQLServer：关键字“用户”错误代码附近的语法不正确：156

Question

I'm doing a desktop application using javax swing, but I'm getting an exception when trying to login to the application. The error is as follows:

Exception Message :

The entity class User consists of these attributes: ID(which is set to auto-incremented), username, password and RoleID(foregin key).

The code which controls the selection in the database is as follows:

public User loginByUsernameAndPassword(String username, String password) throws HealthCareSkdException {
        try {
            Query query = 
            em.createQuery("SELECT u FROM User u WHERE u.username = :username AND u.password= :password");
            query.setParameter("username", username);
            query.setParameter("password", password);
            return (User) query.getSingleResult();
        }catch(Exception e) {
            throw new HealthCareSkdException("Msg! \n" + e.getMessage());
        }
    }

And the login button:

private void loginBtnActionPerformed(java.awt.event.ActionEvent evt) {                                         
        try {
            String username = usernameTxt.getText();
            String password = new String(pwField.getPassword());
            UserRepository repo = new UserRepository();
            User user = repo.loginByUsernameAndPassword(username, password);
            if (user != null) {
                new MainForm().setVisible(true);
                this.setVisible(false);
            }
        } catch (HealthCareSkdException exe) {
            JOptionPane.showMessageDialog(this,exe.getMessage()+"");//exe.getMessage());
        }
    }    

I really don't know what the problem is the code above is the exact code which was used by my Instructor, I tried to run his code too but it doesn't do anything when it's supposed to open up another frame.